4x100m Freestyle (pronounced four by one hundred meter Freestyle) is a real-life Olympic event that can be played in Mario & Sonic at the Olympic Games. It is under the "Aquatics" category, along with 100m Freestyle, and plays somewhat similarly to 4x100m Relay. Four teams of four players take turns to get past the 100m pool four times first. This game requires both speed and stamina and features all sixteen playable characters.
The controls of the game are very similar to that of the 100m Dash event. The Wii Remote can be used on its own, or with the Nunchuk. Before the event starts, the player is given a certain swimming style (example, Vector has the Crocodile paddle). The way to swim is to shake the Remote and Nunchuk in a certain direction (see 100m Freestyle for more details). There are five swimming styles.
When the event starts, the player has to hold the B Button while READY appears on the screen, to build up energy. When GO appears, the player has to release the B Button and flick the Wii Remote down, to get a speed boost. The sooner this is done, the better the boost, but doing it before GO appears will result in a Foul, and will slow down the player, rather than speed them up. Once in the water, the player has to use one of the above swimming styles, which will be shown when the player starts swimming. The faster the controllers are shaken, the faster the player will swim. However, more energy is used up the faster the player swims, and if all of the players energy is burned up, they will stop in one spot, and waste time. To combat this, the player has to press the B Button before the Stamina meter drops to zero. Perfect timing will give the player more speed, but bad timing will slow them down.
 Swim Styles
Four team members take turns to swim two lengths each. Each player should touch the wall before the next player dives in. The first team to have all four members complete two lengths wins.